In the prior art, a wood-like decorative sheet having a figured grain is used as a surface material of the furniture, building, ceiling and floor. As shown in FIG. 1, the conventional ordinary wood-like decorative sheet 11 is fabricated in such a manner that a grain pattern portion 13 and a vessel pattern portion 14 are printed by rotary photogravure on one surface of a colored base film layer 12, and by laying a transparent film 15 on this assembly, a thermal lamination is conducted so that the transparent film 15 is bonded to the colored base film layer 12 while at the same time embossing the uppermost surface of the transparent film thereby to form an embossed depression 16. Also, the surface of the colored base film opposite to the surface thereof printed with the grain has an adhesive layer 17 and a release sheet 18 for attachment to the base material (See Japanese Unexamined Patent Publication No. 2001-260299, for example).
The grain pattern is defined as a pattern representing an annual ring, cross grain or straight grain in the cross section of a natural lumber, and the vessel pattern as a pattern of vessels for sending the moisture and nutrients absorbed from the root to the upper portion in a plant tissue. The vessel pattern is a more detailed design than the grain pattern. Generally, the grain pattern of the natural lumber is the collective name of the annual ring, the cross grain and the straight grain. In this specification, however, the grain pattern and the vessel pattern are discriminated from each other as described above.
In the wood-like decorative sheet described above, the stereoscopic appearance is created by reproducing the cross section of vessels by forming an embossed depression on the surface thereof. The physical roughness formed on the decorative sheet by thermally embossing the surface thereof to create the quality sense such as the grain, however, disappears when the decorative sheet is used in an environment higher than 70° C. in temperature or in an elongated form. This decorative sheet, therefore, finds no suitable applications in producing a thermally molded part heated at the time of attachment or the interior of automobiles used in a high temperature environment.
A method has been proposed in which a frosted transparent coat layer containing particles of a frosting agent in the transparent resin is formed on the surface of a base material to hold the embossed state (See Japanese Patent No. 3150439). In order to reproduce a low gloss of not more than 10, however, the content of the frost agent particles is required to be increased, in which case the holding power of the resin is reduced, with the result that the particles of the frosting agent easily come off or are easily separated and a sufficient performance cannot be exhibited.
A conventional case has also been proposed which uses a thermosetting resin to improve the surface performance of the decorative sheet (See Japanese Patent No. 3576237, for example). Due to the bridging structure of the thermosetting resin, however, no elongation is exhibited in the thermal molding process and the stress often remains after molding with the result that the spring back is inconveniently caused after attachment, thereby making impossible the application in the three-dimensional molding process.